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scale in Preps. 63—69. It will there be noticed that it is
unnecessary, as a rule, to isolate the diazonium salt, but that
the substance is prepared in solution, and is decomposed by
the specific reagent.
With few exceptions, all aromatic compounds which contain
a nuclear amino-group may be diazotised. At the same time
there are notable differences in the ease with which the process
is effected
Toluene from Toluidine.—It is often desirable to obtain
the hydrocarbon from the base. The process of diazotisation
offers the only convenient method. The diazonium salt may be
reduced by alcohol (Reaction i, p. 162) or, as in the present in-
stance, by sodium stannite. Less direct methods are the con-
version of the diazonium compound into (i) the hyclrazine (see
p. 174), (2) the acid and distillation with lime (p. 300), (3) the
halogen derivative and reduction with sodium amalgam, or,
finally (4) the phenol and distillation with zinc dust.
/-CresoL—This reaction resembles that of nitrous acid on
an aliphatic primary amine ; but the liquid requires to be
p-Chlorotoluene, p-Bromotoluene.-—The action of cu-
prous chloride, bromide, and cyanide on diazonium chlorides was
discovered by Sandraeyer, and is known as ' Sandmeyer's re-
CBII3N.,.C1    = CJL.C1    +  No.
C0II5NfrBr    =  CGII5Br    +   N0~
C0HaN2.CN  = Q.IInCN +  No.
Some of the cuprous chloride compounds of the diazonium
salts have been isolated and analysed, and correspond to the
formula CGHr,N2CLCu.>Cl2 (Hantzsch). The formation of a
crystalline copper compound is rendered very evident in the
present preparation. A modification of Sandmeyer's reaction
is the introduction of precipitated metallic copper in place of
the cuprous salt (Gattermann).                                       *•